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Researchers in South Korea for the first time have cloned a human embryo and destroyed it to cull its stem cells.

In the procedure, an embryo that is the genetic twin of a particular patient is grown in a test tube and killed to supply master stem cells that can grow into any tissue — without being rejected by that patient’s immune system.

Scientists have used stem cells obtained from cloned mice to partially cure laboratory mice with an immune system disease. They know how to cull stem cells from human embryos left over in fertility clinics, offering the potential of cell therapy but not patient-specific treatment.

But attempts at cloning a human embryo in the stem-cell quest have failed until now.

Scientists from Seoul National University report that they have succeeded — thanks, they say, to using fresh eggs donated by South Korean volunteers and finding a gentler way of handling the genetic material inside them.

The report appears tomorrow in the journal Science.

The research provides long-anticipated proof that the technique used in mice works on human cells, said stem-cell researcher Dr. Rudolf Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Mass.

“That’s an important point to prove,” he said.

Dr. Jaenisch, however, said that “it’s not of practical use at this point,” stressing that years of additional research are required even to perfect the technique.

The cloning technique still doesn’t work well: The Seoul team collected 242 eggs, from which they succeeded in cloning 30 blastocysts — early-stage embryos containing a mere 100 cells. From those, they harvested one colony of stem cells.

Additional experiments by the Seoul team suggest that its stem-cell colony indeed can generate numerous types of body cells. It began to form muscle, bone and other tissues in test tubes and when implanted into mice.

The team’s next step, which is under way, is studying how to direct which tissues those cells form, said Dr. Woo Suk Hwang, lead author of the report.

Some scientists say the technique offers the potential of breakthrough treatments for diabetes, Parkinson’s and other diseases, but even when the technique is made more practical, any therapy derived from it would be years away from being tested on people.

The experiment is sure to revive the furor over human cloning, in the United States as well as internationally.

It’s likely to renew debate over whether human cloning should be banned. In Congress, the House last year voted to do that, but the Senate stalled over whether there should be an exception for cloning intended for research rather than producing a human being.

The United States is pushing for a U.N. ban on human cloning, but the General Assembly recently postponed a decision. There is almost universal support for a global ban of cloning intended for reproduction, but Britain and several other countries want a research exception.

Most U.S. scientists won’t be able to experiment with the Seoul researchers’ new stem-cell line, because culling stem cells from embryos kills them, and President Bush has forbidden any federally funded research on stem cells from embryos destroyed after Aug. 9, 2001.

Laurie Zoloth, professor of medical humanities and bioethics at the Feinberg School of Medicine at Northwestern University, said the United States needs to pay close attention to such work.

“It is clearly time — now that it is more tangible — to set in place a process where we can have some kinds of experiments supported and some things banned,” she said.

“The kind of cloning to make human babies is impermissible. Clearly, the [South Korean researchers] intent is to do therapy. It’s one tiny step closer to some medical use. It would be a wise thing to support.”